One thing that bothers me in films, be it number 2 films or remakes is when the voices are completely wrong. I don't think the voice for Zazu works at all in LK2 for example but i can over look it as its only a very small part.
They did such a fantastic job the first time around its going to be hard to live up to the legend.
I have never heard of Donald Glover before (or if I have seen him in something i don't know him by name) so i don't really know if this is a good thing or not. From the comments above it seems to be considered a good choice but I am so glad Mufasa is going to be done by Earl jones as his voice is so iconic in the film i don't see how it would work without him, it just wouldn't feel right. The voice I'm worried about is for Scar. He's one of my all time favourite bad guys and it will just kill the film for me if his voice is wrong. Not necessarily Jeremy Irons, although i would love it if it was, but it has to be right. An unconvincing bad guy would kill the film in my opinion.
Whatever happens in all the LK brand so far they haven't made any disastrous choices so I have faith that whoever they have picked and will pick will work out all right in the end.
Ps.
Oh and Whoopi Goldberg made an excellent Hyena, just saying
